Signal controlled inverter-power amplifier



Sept. 10, 1963 J. R. COLE ETAL SIGNAL CONTROLLED INVERTER-POWER AMPLIFIER 6 Sheets-Sheet 1 Filed Dec. 8, 1961 Sept. 10, 1963 J. R. coLE ETAL SIGNAL CONTROLLED INVERTER-POWER AMPLIFIER 6 Sheets-Sheet 2 Filed Deo. 8, 1961 JIMMY R. COLE JOE W WALTON ATTORNEY 6 Sheets-Sheet 3 J. R. COLE ETAL SIGNAL CONTROLLED INVERTER-POWER AMPLIFIER Filed Deo. 8, 1961 Sept. 10, 1963 INVENTORS JIMMY R. COLE JOE I4. WALTON BY ATTORNEY Sept. 10, 1963 J. R. COLE ETAL SIGNAL coNTRoLLED INVERTER-POWER AMPLIFIER Filed bale.

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SIGNAL CONTROLLED INVERTER-POWER AMPLIFIER Filed DeC- 8, 1961 AND /3-3 "OFF" 6 Sheets-Sheet 5 ii l' n w I l WW1 w al 5 l W* I? figg; I@ :wl-fz; tw 1L, 7 /asez (f) il INVENTORS JIMMY R. COLE JOE W WA/ TON ATTORNEY Sept. .10, 1963 .1. R. COLE ETAL SIGNAL coNTRoLLED INVERTER-POWER AMPLIFIER 6 Sheets-Sheet 6 Filed Dec. 8, 1961 nlmwhw INVENTORS J/MMY R. COLE JOE W. WALTON BY TTORNE Y United States Patent() A 3,103,616 v SIGNAL CONTROLLED INVERTER-POWER AMPLIFIER v Jimmy R. Cole and Joe W. Walton, Ponca City, Okla.,

assignors to Continental Gil Company, Ponca City,

Ukla., a corporation of Delaware Filed Dec. 8, 196i, Ser. No. 153,081 17 Claims. (Ci. S21- 45) The present invention relates to alternating current power amplifiers, and more particularly, but not by way of limitation, relates to a circuit device which may be termed a signal controlled, synchronous inverter for converting highpower direct current to high-power alternating current having a frequency corresponding to a lowlevel, variable frequency, alternating current control signal.y

More specifically, this invention is related to electrical circuitry for driving electromagnetic transducers of the type used in mode-rn geophysical equipment. U.S. Patent No.V 2,989,726 issued to lohn M. Crawford and William E. N. Doty on lune 20, 1961, discloses la method of seismic exploration which uses nonrepetitive seismic signals of known frequency content and magnitude rather than the random frequency content of the seismic signal produced by the more conventional explosive char-ge.

The nonrepetitive seismic signal `of Aknown frequency content is reflected from subsurface interfaces and is easily distinguished from other interfering noise to produce easily readable and highly reliable seismic data.' The nonrepetitive seismic `signal may comprise, for example, frequencies from 20 to 100 cycles per second, starting at the low frequency and increasing at a uniform rate over a short period lof ltime to the higher frequency. It has been Afound thatelectroinagnetic transducers similar to large Aloud speakers provide an excellent means for imparting the seismic signal to the earth. However, these transducers must necessarily 'be large in order to induce sufficient energy into the earth that the signals will be refiected from deep subterranean strata. Frequently it is necessary to employ a plurality of transducers operated simultaneously and in synchronism. The problem of supplying electrical power to drive the electromagnetic transducers is formidable because, as with most geophysical equipment, the electrical power equipment must be readily portable, very rugged and always reliable.

' The obvious method for driving a plurality of electromagnetic transducers Wit-h synchronized, non-repetitive signals of yknown frequency content is to generate an electrical signal from a single source, amplify the signal through Ia power amplifier oramplifiers, and supply the amplified signal to the electromagnetic transducers. Un- Ifortunately, the size o-f the synchronized power amplifiers becomes prohibitive when more than a few electromagnetic transducers are operated simultaneously.

Vacuum tube type power amplifiers do not warrant serious consideration because of large size and lack of ruggedne'ss for portability. Heretofore inthe art, the -most 'satisfactory power amplifier source employed varions combinations ;of transistors connected with the load to form la bridge. Some type of control circuit was providedto switch the transistors in the bridge by pairs alternately from cutoff lto saturation and back to cutoff in synchronismy with the control signal thereby ice particularlyk well adapted for use in a controllable fre# quency power supply for driving electromagnetic transducers used in geophysical work. The inverter device employs a semiconductor device having a much higher power rating than presently available transistors. The devices are known in the art as controlled rectifiers, and in the most popular presently available form, are kno-wn las silicon controlled rectifiers and lare therefore casually refer-red to in the art as SCRs, .as will hereafter be the case in this specification and some of the appended claims. rFhe controlled rectifiers used in connection with this invention, have what is conventionally termed an anode, a cathode and a gate, which are labeled in FIG- URE 7 which is an enlarged View of the conventional Isymbol used in the art to represent a control-led rectifier; The conventional forward direction `across the controlled rectifier is from anode to cathode. The operating characteristics lof the controlled rectifier are such that the device will, for all practical purposes, block current in both the forward and reverse ydirections within the forward and reverse breakover and breakdown voltages. In this state, the controlled rectifier is said to be cutoff or ofi However, when a positive trigger pulse of relatively low potential is applied to the gate, the controlled rectifier will turn on and con-duct in the forward direction with substantially no impedance when a potential is applied from anode to cathode. The controlled rectifier will continue to conduct -in the forward direction until the forward potential is reduced substantially to zero by either removing the forward potential or by applying 'a reverse bias to overcome the forward potential for a short period of time. However, in order to switch the contnolled rectifier to cutoff in a minimum of time, a reverse bias must be applied for a short period of time. Additional detailed information concerning the operating characteristics of the SCR device may .be obtained from Controlled Rectifier Manual, published Iby General Electric Company in 1960.

In accordance with the present invention, `four ccntrolled rectiiiers are connected to form a bridge with the load to be driven. This may be 'accomplished by connecting the first controlled rectifier, the first terminal of the load, and the fourth controlled rectifier in series in the forward direction across a `direct current power source, such as a battery. Similarly, the second controlled rectier, the second terminal of the load, and fthe third controlled rectifier are connected in series in the forward direction across the direct current power source. Then by #alternately turning the first and third, thenthe second and fourth controlled rectifiers 0n, the direct current from the power source will be directed first in one direction and then in the other direction through the load. The present invention also contemplates la novel circuit for synchronizing the switching of the controlled recitifiers with a variable frequency control signal so that the frequency content of the alternating power current through the load will correspond with that of Ithe control signal. It is further contemplated by the present invention to provide a novel circuit means for reverse biasing the several controlled rectifiers of the bridge to cutoff condition by utilization of fthe energy stored by la capacitor. It is also within the purview of this invention to provide several alternative circuit means for applying the energy or stored 'charge fon the capacitors which are utilized to reverse bias the several controlled rectiiiers.

Therefore it is an important object of the present invention to provide an improved inverter device for con- Y invention. i

FIGUR-E 4 is a schematic circuit diagram of still aning a greatly increased power ratingland which is' there?. y' fore particularly adaptadas aV power supply tor 'driving electromagnetic transducers used `in Vgeophysical-explora j tion'. i Y

Another important object of the present invention fis to provide an inverter device ofthe type describedwhich produces a square wave alternating current from .a direct Y Y Y current power source whereby` the square wave 1will have maximum power Vfor the given maximum voltage ofthe direct current power source.k t l Another important object of the present invention 1s to provide an inverter device of the type Ydescribed which` f is capable of'produeing anv alternating currentnanging in requency rfrom zero, or -direct current, tofseveral hundred cycles per second.` Y 1 Y Another important object of theY present invention ris `to provide an inventer device of the type described khaving an extremely low output impedance. Y

Another important object of the present invention isV Another important object ofthe present inventionfis yFIGURESSand 6 are awseries fof graphs'illustratingV j Y thevarious potentials Vinduced inthe sec'on'daryrwindings` t of ythe contro-i"Y transformersV andthe time relationgther between when Vsquare ywave control signals and `sinusoidal control,signa1s,1respective1y,.are @usedto kcontrol the vany V v ousinverterdevices of the'presentinventionV i? Y Y presentfinvention. 1

VA standard.electricalcircuit,symbol forraslicon coni.

trolled rectiieror `SCR is shown in FIGURE`7. The

FIGURE 7V is` a .ldiagram'offthe conventional symho Y Y usedrto designate a. fcontrolled-rectier^orSCRnsed in Y the inverter. devicesrconstructed in vaccordance with the semiconductorfdevice'has :an anode terminal, `a cathode; .f l

terminal land o a gateterminal as' labeled.v 't .The conventional forward; direction is from anode to cathode. K The J SCRfcan .fbe Vtriggered Von` Vby making the gatefizrositive with respecta-to the'cathode. `Then when ,a io'rwardpo'- tential is applied, Le., when the Vanode is made more Y to provideY a simple and reliable circuit for reversebias- Y ing la controlled'trectiier using a sourceY of potential of Yno greatermagnit-ude'than the potential applied in Jthe `forward direction across the rectifiedr and in most cases Y using the same direct current potential.

VAnother.',irnportant object Yof the present invention isl Y to provide an inverter device of ,thetype' described in-A Y which the components in the control circuitry for Switcllfy ing the controlled reotiers'tocutotftmay ,be reduced to minimum power ratings f 'Another importantohject of the present,invention'isr i torprovide an inventer device of the typeldescribed which Y t may be operated, 'except for the control signal, entirely l by an altematingfcurre'nt Vpower source such as "a" threephase alternator. Y 1

l Another object of the present invention isjto provide an inverter device" of the typewrdescribed which utilizes.Y a Ilow-level control signal'fosrVV reverse biasing the` controneo reetiners to cutofneondition Many additional Vobjecrtsrand advantages ofthe present invention will be evident to those skilled in the art from Vthe following detailed description ofthe preferred ernbodirnents illustrated inthe drawings.

f In the drawings:

FIGURB'l isV a schematic circuit diagnarn of an-.ing kverter device constructed in. acccnrlanceV with the present invention. V u n v Y Y FIGUREy 1A is a schematic Ydiagram of actnitrol`cir-V cuity 'which may be `used Yin* combinationY `with theY iniverter .devices of FIGURES V1,i2, 3 yand 4and impartien- URE 1. Y Y Y FIGURE `2. is a schematic circuit diagfnam ofv another inverter device constructed in accordance with Ythe present invention Vwhich can be driven by a fully rectified alternating cunrent 'power source.

- FIGURE 2A is a schematic `diagram of a part of a control circuit for inverter devices in accordance with the present invention and in particular should Ibe considered in combination with FIGURE 2.

`FIGURE 3 is a schematic circuit diagram of another inverter device constructed in accordance with the present other inverter device constructed in accordance with the present invention. t

V FIGURE 4A is a schematic circuit diagnam which i should -be considered in combination with FIGURE 4.

Y, in shaun be considereukip 'samenvatten with FitG-Y 1 positive than the cathode; the 'SCRrwill conduct in the forward direction.

gate is not maintained positive with respect to the cathode. y, rReferring now to FIGURE l, a direct current power source, .such as battery '11, is connected across apositiveKV power terminal 12 Yand .a .negative power terminal '174r `of Y"an inverter device 10. A load '1;610 be driven by the inverter device 10 has first and second load terminals 'Y 18 andV 2t).r rIheloadY 16 may -be the coil of an electromagnetic transducer used in` seismog'raphicsurveying. A iirst power SCR P-lY is connected in .the Vforward direction between thepositive ypower terminal 'lf2 and.V

Vthe tirst load` terminal; 18. `A fourth'poweri-SCR P-lft,V

` is connected in the forward directioubetween the first 'Y `*load* terminal '18.and 'the negativepower,terminal114if A second power `SCR P92 VisV connected` in Vthejforward4 'i directiou'between the positive ypower .terminallz and the 1 second loadsterminalzt), 'antifa third powerV SCR P93 isfconnected in the forward'direction between` Vthefloaul.

terminal 20, "and `negatil/power terminal :14. t

The four power SCRs are connected to the load16in` such va'rnanner as, toform whatmayube `terineda power Vbridge. When the odd-numbered power SCRs Pfland.V

P-S are turnedV on` Vand the even-numbered SCRs,P'-2

:and 1?-,4 turned o a directh current 1:1 from the battery Y SCRrP-S. Then when the power SCRs P-l and P-3vare turned off and the power SCRsfP-Z and P-4 are turned Y fonfa current I-f2 will dow through SCR P4; through jy Y the load-1 6V, and through SCRE P44 :inthe ydirection indij cated bythe arr-owenl lnthis manner theunidirectional` ordireet current of Vthe battery power source `llfis con?,` Y

vertjedY to a bit'iirectional:Y or a'lternatingilcurrent through` q the load 16; f Theealternating current Vthrough the .load'ff 16 willV havear frequency :corresponding to the "irate atl whichtherst-and third and thefsecon-dfand Vfourth power SCRsare switched fon and ,off as described.

As previously mentioned the power SCRs are easily switched fromv the current locking or .cutorl state to the conducting or on lstate by a trigger pulse of positive potential applied to the gate, the potential at the gate :being positive with respect to thecathode. Then any positive potential applied in the forward direction from anode to cathode will cause a current to flowin the forward direction thro-ugh the SCR. Therefore, the sec-V The SCR can lie/reverse biased toY cutoff Vby making the cathode moreV posi-tive than the ano-defer a short period of time, provided: ofcourse the Although i-t is a relatively simple matter to switch the power SCRs on, it is far more -diliicult to switch them offf As previously mentioned, in order to turn the SCRs off in a minimum time, which isvirtually essential in `the present application `as hereafter explained, the respective SCRs must be reverse biased by driving the cathode of the SCR more positive than the anode. The period of time during which the SCR must be reverse biased is relatively short, but does require a tinite time, as hereafter explained in greater detail.

A reverse bias loop circuit comprised of a capacitor C-l and a reverse bias SCR RB-l is connected across the anode and cathode of the power SCR P-l. It will be noted that the reverse bias SCR RBdl is connected in opposition to the power SCR P-l in that the cathodes and anodes of the two SCRs are connected to each otherv in the reverse bias loop circuit. Similarly, a reverse bias loop circuit is provided for power SCR P-Z comprised of a capacitor C-Z and Ia reverse bias SCR RB-2. The reverse bias circuit for the power SCR P-3 is `comprised of the capacitor C-3 and the reverse bias SCR RB-S. The reverse bias circuit for the power SCR P-4 is comprised of the capacitor C-t and the reverse bias SCR RB-. In each case it will be noted that the respective reverse bias SCRs are connected in :opposition within the reverse bias loop circuit to the respective power SCR.

A charging circuit is provided for charging each of the capacitors C-al, C-Z, C-3 and C-4 to a potential of a polarity and magnitude sufficient to the reverse bias the power SCRs when discharged. The capacitor charging circuits comprise the primary winding 30` of a rst autotransforrner AT-1 which is connected between the rst load terminal i8 and the load 16 so that both currents I-l and L2 will pass through the primary winding 30. The secondary winding 32' of the first transformer AT-l is connected through a diode D-1 to charge the capacitor C-l by means of the charging loop circuit starting at the first load terminal 18, through the diode D-1, Vthe capacitor C-1, through the power SCR P-l, which will be turned on during the charging period as hereafter described, and back to the iirst load terminal 1,8. The polarity of the primary and secondary windings 30 and 32 is as indicated by the symbols when the power SCRs P- and P-2 are conducting the current I-1 through the primary windings 30. Therefore, the current induced in the secondary windings 32 will pass through the diode D-d and charge Ithe capacitor C-l to a polarity indicated by the symbols. Of course, the current in the secondary windings Vwill be introduced only during the rise of the current l-l as the power SCRs P-1 and P-Z are switched on As the current I-l falls, the diode D-l willprevent discharge of the capacitor C-1 through the charging circuit. Similarly, the reverse bias SCR RIB-1, which blocks current in either direction when in the cutolf state, prevents the capacitor C-l from discharging through the reverse bias circuit until the reverse bias SCR RB-ll is turned on, at which Vtime the capacitor C-1 will discharge to reverse bias the power SCR P- to cutof, as hereafter described in greater detail.

A similar charging circuit is provided for charging the capacitor C-Z. The primary winding 34 of a second autotransformer ATi-2 is connected betweenthe load 16 and 'the second load terminal 20. The secondary Winding 36 of the autotransformer AT-2 is connected through a diode D-2 to charge the capacitor C-2 during the rise of the current 1 2 as hereafter explained. The charging circuit for the capacitor C-3 is comprised of the secondary winding 36 of the transformer AT-Z which is connected through a diode D-Swto charge the capacitor C-3 duringrthe rise of the current -I-1. lIt will be noted that the diode D3 is reversed with respect to the diode D-Z so that current generated in the secondary windingv 36 will pass alternately through the diode D2 or the diode D-3 depending upon whether the current I-1 or I-2 is passing through the primary as hereafter described in detail. Similarly, the charging circuit for the capacitor C-4 comprises the secondary winding 32 of the rst autotransformer ATAI which is connected through the diode D-ft to charge the capacitor 0 4. It will also be noted that the diode D-4 is reversed with respect to the diode D-l. v

When the power SCRs lL-ll and P-3` are turned on, the current I-l will Iflow through the load andthe primary windings 30 and 34. A polarity will be linduced in the secondary windings 32 and 36 as indicated by the symbols during the rise of the current I-1. This polarity current in the secondary windings 32 and 36 will then charge the capacitor C-l to the polarity indicated through the loop circuit including the diode D-1 and the power .SCR P4. Similarly, the current induced in the secondary winding 36 will charge the capacitor C-3 through ther diode D-S and the power SCR P-3` to the polarity indicated by the symbols. In each case the charge will be retained on the respective capacitors by operation of the diodes D-l and D-3 and the reverse bias SCRs RB-l and RB-3` until such time as the reversed bias SCRs are turned on as hereafter described. When the power SCRs P-1 and P-`3 are turned off and SCRs P-Z and P-l are turned on, the current 1 2 will flow through the load 16 and the primary windings 30 and 34. A current will then be induced in the secondary windings 32 and 36 having a polarity opposite to that indicated by the symbols. The current induced in the secondary winding 36 will pass through the diode D-2 and charge the capacitor C-Z. The power SCR P-Z completes this charging loop circuit. The diode D-2 and reverse bias SCR RB-.I prevent the capacitor C-2. from discharging. Similarly, the current in the secondary winding 32, which is opposite in polarity to the symbols, will charge the capacitor CA4 through the diode D-4. Of course, the diode D-4 and the reverse bias SCR RB-4 will prevent the capacitor C-4 from discharging.

In order to control the instant at which the respective capacitors C-1, C-Z, C-3` and C-4 discharge to reverse bias the respective power SCRs to cutoff, the secondary windings of transformers TRB-1, TRB-2, TRB-3l and TRB=4 are connected between the gate and cathode of the respective reverse bias SCRs. Therefore, merely by applying a current to the primary winding of the respective transformers TRB (see FIG. 1A) `of the proper polarity, a positive trigger pulse can be applied to turn on and the respective capacitors discharged, the potential across the respective kreverse bias SCRs will reduce to zero and the SCRs will revert to cutoff in preparation for the next charging cycle.

Therefore, from the above description it will be seen that in order to produce an alternating current through the load 16, it is necessary to sequentially: (l) trigger the power SCRs P-l and P-3 on by a positive pulse induced in the secondary windings of the transformers TP-il and TP-3; (2) trigger the reverse bias SCRs RB-1 and RB-3 on to discharge the capacitors C1 and C-3 and reverse bias the power SCRs P-1 and P3 to cutoff; (3) trigger the power SCRs P-Z and P-4 on by a positive pulse induced in the secondary windings of the transformers TP-Z and TP-4; and, (4) trigger the reverse bias SCRs RBJL and RB-4 on to discharge the capacitors C-Z and C A- and reverse bias the power SCRs P-Z and P-4 to cutoff.

A control circuit for switching the inverter device 10 of FIG. 1 in synchronism with a control signal is schematically shown in FIG. lA. lt will be noted that the eight transformers shown in FIG. lA have reference characters corresponding to the transformers of IFIG. l; V

A square wave alternating current basic control signal which may be generated by any suitable source, is

passed through a phase inverter 42 to produce ii-rst and second alternating current secondary controlV signals 44 and 46. It will be noted that the signal 44 is identical to the basic control signal 40 both as to phase and shape,

as can be seen by a comparison of the time points To through T5.' However, the secondary control signal 46 is l,180 degrees out of'phase with the secondary control sig- `nal 44 and therefore with the basic control signal 4d. Thercontrol signal 44 is 'passed through a class C amplifier 48Vwhich produces ay control signal Sil havingponly positive square-shapedpulses between* times T-T1, TZ-Tg and 'F4-T5, as indicated in FIG. lA. The signal 46 is fed through a similar class fC ampliiie-r Y52 to produce a control signal 54 having positive pulses which alternate in time with the positive pulses of the control signal Sil,

the lsquarefshaped positive pulses being between times Tl-TZ andTa-Tg as indicated in FIG. lA. The preferred shape of the'control signals Sil-and 54 are shown in greater detail in FIG. and are hereafter :described in greater detail. a The control signal Sil Vis applied Yto the primary windings ci the transformers TP-l and TRB-1 which respectively turn the power SCRv lP.- 1` on and loff, and transformers 'TP-3 and TRB-3, which respectively turn the power SCR P43` onl and 1o Similarly, the control signal54 is; connected to the primarywindings of the ktransformers TP-Z and ,TRB-2, which respectively turn power SCR P-Z fon and oij and trans- `iormers yT13-4 and TRB-4 which respectively turn power SCR P-4 on and 05. y Y i The polarity of the secondary windings of the transformer TP-1 with respect to the primary winding is such that during the rise times To, T`2Vand-T4Y of the control signal S0, a positive pulse will be induced in the second- .Y

arywinding 21 which will be applied to the gate of the power SCR P-1. Therefore, upon each riseof the signal 50, `a positive Vpulse will be induced in theY secondary windingj'20 approximately at times To, T2 and Trai-1d the "oti at each of these times. Therefore, the power SCRV P1 is turned off at time T1 and remains off until time T2. In this respect it will be noted in the drawings that when the polarity dots such as 56, are matched as in transformer TP-l, a positiverpulse will be induced in the secondary winding during the rise of the current in the primary winding. Accordingly,in transformer TRB-.4, where the reference dots `5S are arranged oppositely, a positive current will be induced in the secondary winding yduring the Ifall of the signal vcurrent in vthe primaryY winding.

Since the' same control signal 5t) is applied to the primary winding of the transformer 'FP-3, a positive trigger Vpulse will be -induced in the secondary winding 23 of the transformer TYP-S at times To, T3 and T5 in exact syn- 'ohronization with the trigger pnl-se induced in the second- A'ary winding 21 ,of transformer TP-1. Therefore, the power SCR P3 will be turned on simultaneously with power SCR llLl. The'same control signal 50 is' applied to thep'rirnary winding orf the transformer TRB-3, but as in the case of transformer TRB-l, thesecondary winding is reversed so` that a positive trigger pulse is induced during the fall :of the current to trigger the reverse` bias KASCRs ARB-l and RB-S on at times T1, YT3 and T5, and Vthereby reverse bias the power SCRS rP--1 Yand P-3 to outo Therefore, thepower SCRs P-l and P-S are turned fon and off in precise synchronization.

As previously mentioned, the control signal 54 is applied tothe primary windingof the transformer T2. A positive trigger pulse will be induced i-n the secondary windings 22 during the rise of ther control signal current at times T1 and T3 and, sincerthe secondary winding 22 is connected to control the power SCR P-Z, the power SCR P-Z will be turned on at times'Tl and T3. Simila-rly, a positive trigger pulse is induced in the secondary Winding of the translforrner TRB-2 during lthe fall times T2 and T4 to turn the power SCR P-Z nii In the same manner, positive trigger pulses are induced in fthe secondary windings of the transformer TP-4 by the control signal 54Y at times T1 and T3 to turn the powerrSCR P-4 cirg and positive trigger pulses are generated in the sec- Y ondary winding lof the transformer VTRB-4 at times T2 and T4 to trigger the reverse'bias SCRs RB-2 and R13-4 on and thereby reverse bias the power SCRs P-Z and .P-4 to cntofhV Therefore, it will be seen that during time period TU-T1, the power SCRsP-l and P- are turned on and the power SCRs P2 and P-"4 remain oft to produce a current 'I-1 through-the load 16; and

. during time T1.-T2,-the Vpower SCRs P-2 and P-4 are turned on and the SCRs Pland P-IiV are reverse biased to cutoff to direct the current I-2 through the load.

In summary, when the direct current power source, such as the battery lll, is connected across the power terminals l12 and 14, no current will flow through the load 16.` However, when `the control signals 50' and 52 are applied to the primary windings or the eight control transformers shown in FIG. lA, the inverter device 10 will operate as ,followsc` At Vtime TD-the positive trigger pulse induced Yin the secondary windings 2,0' `and 23 of control Y transformers TP-1 andTlfS willbe applied ta` the ga-tes of the power'SCRs P-1 and P43 to switch the power vS-CRs on Current I-1 will theuflow through SOR Th1, through the primary winding 30 of the autotranstformer AT-l, through the load 16, through the primary Y winding 34 of the autotransformer AT42, and through the power SCR P-3. TheV current I-1 flowing through the primary winding of the autotransformer AT-l will induce a current in the secondary winding 32 having a polarity as indicated. This induced Vcurrent will pass through the diode D-1 and charge the ycapacitor C-l through the loop charging circuit including the SCR P-1. Of course, only the rise of the current Iel when it is first turned on charges the capacitor C-l, and the chargeis maintained on the capacitor C41 by operation of the diode D-1 and the fact that the SCR RB-il is cih Similarly, the current induced in the secondary winding 36 of autotransformer` AT-Z is of va polarity indicated by the symbols so that the i capacitor C-3 is charged .by conventional current passing through the power SCR P-3 to the capacitor CdS, and through the diode D-3 back to the secondary winding 36. The charge on Vthe capacitor C-S will be retained by the diode D-3 and the reverse bias SCR lRBJ, which is oif At -time T1 a positive trigger pulse will he induced in the secondary windings of the transformers `TRB-3 and TRB-1 and applied -to the gates of the reverse bias SCRs v RB-`1 and RB -3\. The reverse bias SCRs 'RB-1 and RB-3 `are then turned on to discharge the :capacitors C-l and C-3 and reverse bias the power SCRs P-l and P`3 tothe cutoir condition. When the charge from the respective capacitors has dissipated, the potential across the reverse lbias SCRs RB-1 and RB-S will be reduced to zero and the reverse bias SCRs will revert to cutoff preparatory to the next charging cycle. Almost simultaneously at ltime T1, a positive trigger Vpulse is induced in the secondary windings 22 `and Z4 of the control transformers TIK-2V and TP-4 and are .applied tothe gates of the powerrSCRs P-Z and P-4 respectively, thereby switching the power SCRs on. The current I-Z then passes throughthe load 16 'as indicated, also passing through the primaryV l windings 30 and 340i the au-totransformers AT-l and AT-2.. Since the current inV the primary winding 34 is now 'reversed to that indicated bythe symbols in FIG. 1,

the current induced in the secondary winding 36 of transformer AT-2 will also lbe of reversed polarity. The induced current in the secondary winding 36 pass through the diode D Z and charge the capacitor C-Z, the charging loop circuit being completed through the now conducting SCR P-Z. Similarly, the current induced in the secondary winding 32 is of a polarity opposite to that indicated so that conventional current passes through the now conducting power SCR P-4 to charge the capacitor C-4, the charging circuit being completed through the diode D-4 to the secondary winding 3-2. The diodes D-Z and D-4 prevent discharge of the capacitors C-Z and C4 as do the reverse bias SCRs RB-2 `and RB-4. The current I-2 flows through the load :from time T1 until time T2. At time T2 `positive trigger pulses are induced in the secondary windings of the transformers TRB-2 and TRB-4 by the fall of the control signal S4 and areapplied to the `gates of the reverse fbias SCRs RB-`2 and RB-4 respectively to switch the reverse bias `SCRs 'on. The capacitors C-Z an-d C-4 will then be dischargedto reverse bias the pow-er SCRs P-2 and P-4 to .cuto

This sequence of events will continue so long as the control signals 50 and 54 are applied to the primary windings of the control transformers as described. However, it should be noted that upon cessation of the control signals 50 and 54, all ofthe SCRs will be in the cutoff or current blocking condition. The power SCRs P-L P-Z, P-3 and P-4 will be cutoi by the discharge' of the respective capacitors through the reverse bias circuits. The reverse bias SCRs RB-1, RB-2, vRB-Z: and RB-4 return to the cutoff state merely by reason of the Vfact that the potential across the respective SCRs is reduced to zero upon discharge of the respective capacitors. Although this is the slower method for switching the reverse bias SCRs to cutoiif it is suliiciently tast tor the present application.

From the above description it will be evident that a substantially square wave 'alternating current will be applied to the load 16 to provide maximum power for any given potential ofthe battery power source 10. The square wave alternating power current is in precise synchronism with the input control Isignal 40. The frequency of the alternating power current provided by the inverter device can fbe varied from zero, i.e., direct current, toseveral hundred cycles per second simply by varying the frequency of the low level control signal 40. The upper limit on the power frequency is limited primarily by the period of time required to switch the power SCRs to cutoi after the reverse bias has been applied. In this regard it is desirable that the control signals 50 and 54 have a dwell or delay time between thefall of Ione signal, and the rise of the other signal to assure suiicient time Ifor the power SCRs to 'be reverse biased to cuto as will hereafter be explained in :greater detail in the discussion of FIGURES 5 and 6. 7

Since transformers 'IP-1, TRB-1, TP3 `and TRB-3 are each connectedV to receive the control `signal 50i in their primary windings, it will be evident that a single primary transformer winding with the four required secondary taps could be used. Similarly, the transformers TILZ, TRB-2, TP-4 and TRB-4 could be combined into a single transformer having one primary winding and the required number of secondary winding taps. It is also -to be understood that lalthough the square wave shape of the control signal 40, and therefore of the control signals 50 and 54, is highly desirable for the most ecient switching the SCRs, -a simple sinusoidal signal can #be used as hereafter described in detail in connection with FIG- URE 6.

Eaibodimenr of FIGURES 2 and 2A A second embodiment of the present invention is schematically illustrated in FIGURES 2 and 2A. The inverter device 180 shown in FIGURE 2 is lbasically the same as the inverter device 10 shown in FIGURE l.

However, `an alternating current power source is utilized to charge the capacitors which reverse bias the four powerSCRs of the inverter device 160, and the alternating current power source is converted Iby la full-wave rectifier to direct current to drive the power bridge. Substantially the same components are employed in the inverter device as in the inverter device 10, except that the autotransformers AT-l und AT-2 are eliminated. Therefore, the same reference characters are retained in FIG- URE 2 as in FIGURE 1, with the exception that the eight control transformers of FIGURE l have been consolidated into two control transformers I 'and II having primary windings CT-l and C122 and multiple tap` secondary windings as illustrated in FIGURE 2A. Therefore in FIGURE 2, only the secondary windings are illustrated `and the reference characters have therefore been changed from TP and TRB to SP and SRB, respectively, to designate only the secondary windings, the primary windings being shown only in FIGURE 2A.

Direct current power is applied to the power terminals 12 and 14 by la three-phase power source, such as an alternator 101, which drives 'a conventional full-wave rectifier 102. Power SCRs P-1, P-Z, P-3 and P-4 are connected to the load 16 to form a power bridge las in FIGURE l. When SCRs P-l land P-S lare triggered on a current I-I will pass through the load 16. When SCRs P-l and P-3 are reverse biased oli tand power SCRs P-Z and P-4 are triggered on, la current I-2 will pass .through the load 16. The secondary windings SP-l, SLP-2, S13-3 Iand S13-4 each apply a positive trigger pulse to the gates of the respective power SCRs thereby triggering the SCRs on A reverse bias circuit comprised of reverse bias SCR RB-1 and a capacitor C-1 is provided to reverse bias the power SCR P-1 to cutofl A reverse bias circuit including reverse bias SCR RB-Z and capacitor C-Z is provided to reverse fbias power SCR P-Z to .cutoff. Similarly, la reverse 'bias circuit comprised of capacitor C- and SCR RB-3 is provided to reverse bias power SCR P-3 to cutoffj and a reverse bias circuit comprised of capacitor C-4 and SCR RB-4 is provided to reverse bias power SCR P-4 to cutofff The primary distinction between the arrangement of the reverse Ibiasing circuits of the inverter device 100 of FIGURE 2 when compared with the reverse biasing circuits of the inverter device 1G of FIGURE 1 is that one side of the capacitors C-1 and C4 :are connected directly to the load terminal 18, yand one side of the capacitors C-Z and C-3 is connected directly to the circuit load terminal 20. These connections permit the capacitors to be charged lby the alternating current power supply from the alternator 101 las hereafter described. The phase terminal 1154 of the alternator 1M is connected by leads 106 and 108 to a diode D-3. The circuit continues through the resister R-3 to the capacitors C-3 and C-Z, then through resister R-2 and diode D-Z, Iand leads 110 and 112 to the phase terminal 114 of the alternator 101. A similar charging circuit for the capacitors C-4 and C-1 from the phase terrrn'tnal IEM to the phase terminal 114 of the alternator 101 comprises the lead 106, la lead 116, diode D-4, resister R-4, capacitors C-4 yand C-l, resistor R-l, diode D-1 and leads 118 'and 112.

In order to better understand how the capacitors C-1, C-2, C-3 and C-4 are charged to a potential of a polarity vand magnitude suilicient to reverse bias the respective power SCRs upon discharge thereof, as phase terminal 104 of the alternator 101 becomes positive with respect to the phase terminal 114, all four capacitors C-1, C-Z, C-3 and C-4 will `be charged to ya potential of approximately one-half the peak voltage between the terminals. 'Ilhe capacitors C-l and C4 are charged through the diodes D-4 and D-1 iand capacitors C-Z and C-3 are charged through diodes D-S and D-Z. The polarity of the charge upon each of the capacitors is indicatedV by the charge symbols, which is such as to reverse bias the 11 respective power SCRs upon discharge. When the power SCRs P-1r and P-3 are turned on to cause Y the current I-l to pass through the load 16, the lirst load nal 18 is connected directly to the positive :side of ther` will then be lapproximately equal to the peak voltage of the power SCR P-l. Similarly, as the secondwload terminal V20 becomes more negative, the capacitor C-3, the negative side of which is connected directly to the termi- -nal 20, will also receive Ian additional char-ge as described. Therefore, whenthe reverse biasSCRs RB-l land RB- are triggered on, the capacitors C-1 and C-3 will discharge to reverse Abias the power SCRs P1 and P-3 to cutoff When the power SCRs P-2 and P-4 are triggered on, the second load terminal 20 will become positive and thereby approximately double the charge on the capacitor C-Z, and the first load terminal 18 will become more negative to approximately double therinitial rcharge on the capacitor C-4 in the s-ame lmanner described in connection with the capacitors C-1 and C-3. Then when 'capacitor C-1, the chargeeon the capacitor C-1 will be"` Y Y approximately doubled Ydueto the increase in potential of the terminal 18. The charge on the capacitor C-l' Y, the alternating currentwhich ,is 4suiiicient kto reversebias e f The resisters R-1, R-2, R-3- and R-4 should be sei lected sufliciently large to limit the phase current through the reverse bias SCRs RB-l, RB-Z, RB-3 and RB-t respectively. Current may liow through the reverse bias SCRs after they are triggered on for approximately one-half cycle of the alternator current after the respective' power SCR has been reverse biased to cutotl Therefore these resistersV are highly desirable because they limit this current and lessen the required average current rating for the reverse bias SCRs. The reverse bias SCRs RB-l, RB-2, RB-'Sl and R13-4 will vrever-t to the cutoff statewhen the voltage across each decreases to the-cutoff value.

As previously mentioned, the sequence of operation of the inverter device 100 of FIGURE 2 is identical to that of the inventer device lill of FIGURE 1, and the same control signals 50l `and 54 may be applied to the primary windings CT-l and CT-Z of the control transformers f1 and II of FIGURE 2A. A close comparison of FIGURE 2A to FIGURE lA will reveal that the secondary windings SP-1, SRE-1, SP-3` and SRB-4 are Vthe full equivalent and are arranged in the same order as the transformers TP-1, TRB-J, TP-3 and TRB-'3-.

Similarly, the secondary windings SP-Z, SRR-2, SP-4 and SRB-4 correspond to the transformers TP-Z, TRB-2, TP-4 and TRB-4. Therefore, when the first and second control signals 50 and 54, which are 180 degrees out of phase are applied to the primary windings CT-l and CT-Z of the control transformers I and II, respectively, the sequenceVT of operating events of the inverter device `100 of FIGURE Z is identical tothe sequence of operating events of the inventer device 10 of FIGURE 1 as described previously. However, to summarize operation of theembodiment of FIGURE 2, assume first that alil SCRs are ott During the rst positive half-cycle of the alternating phase current between phase terminals '104 and 114 of the alternator 10'1, the four capacitors C-l, C-Z, C-3 and C4 will be partially charged as described above. At timeTo of the control signal 50, power SCR?s P-1 and P-,S will be triggered on by positive trigger pulses induced in secondary windings SP-1 and SPAS; A rectified yor ldirect. current I-1 will then ow through the iload 16. YThe lirst Iload terminal 18v will become'more' positive and thereby approximately double negative, thereby approximately doubling' the charge on the capacitor `C-3. At time T1 the' reverse bias SCRs RB-l and'RB-.i` are triggered on by positive trigger t f pulses inducedV in the `secondary windings SRB-,l and SRB-S respectively. The capacitors C-1 and C-3 then c discharge to reversecbias the power SCRs P-1 `and Pf3 Y secondary windings SP-J2` and SP-4. A rectilied or direct current VI-Z then Hows throughftheload 16: The second Y load terminal 20 will then become more positive and thereby cause an additional charge on the capacitor C-2. At the same time the first load terminal 18 becomes more negative and places an additional charge on the capacitor C-4. At timeTz, the reverse bias SCRTs BR-Z and RB-'4 Iare triggered on by pulses induced in the secondary windings SRE-Z and SRE-4. The capacitors C-2 and C-4 then discharge and reverse bias the power SCRs P42. and P-4 to cutoff So long as the control signals i 50 and 54 continue, this sequence of events will repeaty to produce a square wave alternating current through the load 16 as hereafter described in greater detail.

Lt will be noted that the fall of the last `positive pulse ofthe control signal Slt willV reverse bias the power SCRs P1 and P-3 -to cutol The reverse biasSCRs R\B-1 and R13-#3r will then revert to cutoff when the potential across each SCR falls to zero. Similarly, the power SCRs VP-Z and P-4 willbe reverse biased to cutoff by the fall of the last half-cycle of the control signal 54,

and the reverse bias SCRs RB-Z and RB-4 will revert Y to cutoff when the potential across each SCR falls to zero. Therefore, upon cessation ot the control signals 50E and 54, all componentsof the inverter device 190 will be .turned offf Y Embodmenz ofVFIG. 3

Y The inverter device Ztltl illustrated in FIGURE 3 hasV FIGURE 3, a suitable direct current power source, such' as a D,C. generator or battery, is connected across the positive power terminal 12 and the negative power terminal 14. The four power SCRs P-1, P`2, lP-S` and n A reverse bias circuit tor the power SCR `P1 is comprised of the reverse bias SCR RB-l and the capacitor.

O-l, which are Iconnected in series across the anode and cathode of the power SCR P-l. A reverse bias'circuit 'for the power SCR PTZ is comprised of the capacitor C-Z and the reverse bias SCR RB2. A reverse Vbias Vcircuit for power SCR P-3 is comprised of the capacitor CeS and the reverse bias SCR RB-3. Similar-ly, a reverse Y bias circuit forA the power SCR P-4 is compri-sed of the capacitor C-4 and the reverse bias SCR RB-4. In each case, it will be ,notedl that the reverse bias SCR isconnected in opposition to the power SCR so that when the respective reverse bi-as SCR is triggered on,- the Ycorre1 sponding capacitor will be discharged in opposition to vdelay as hereafteredescribed, the powcrSCRs P-Z andV P-4 Aare triggered'on by positive' pulses induced in theY 13 the respective power SCR and reversebias the power SCR to cutoffv As in the inverter -device 100 of FIGURE 2, secondary transformer windings SP 1, SP-Z, SP-3 and SP-4 are connected to apply a positive trigger pulse to trigger the power SCRs P l, P 2, P-3 and P 4, respectively, on Secondary transformer windings SEB-1, SRE-2, SRB 3 and SRB 4 are provided to trigger the SCRs R13-1, RB 2, RB-3 and R13-4, respectively, on and thereby reverse bias the respective power SCRs to cutoff A charging :circuit for charging the capacitor C 1 is comprised of the secondary winding STA of transformer TA and a diode D- 1 connected in a loop circuit with the capacitor C 1. The primary winding PTA of the transformer TA is connected through the diode 202 between the r-st load terminal 18 andthe negative power terminal 14. In this connection, the primary winding PTA can be considered as connected in shunt around the power SCR P 4 and also as connected in parallel with the load 16 when the current 1 1 is owing therethrough, as hereafter explained, in greater detail.

The circuitry for charging the capacitor C 2 comprises the secondary winding STB of a transformer TB which is connected through the diode D-2 to charge the capacitor C 2. The primary winding PTB of the transformer TB is connected, through `a diode 2114, between the second load terminal Ztl and the negative power terminal 14. The `diode 204 `and primary winding PTB may be considered as connected in shunt around the power SCR P S and would also be considered as connected parallel with the load 16 when the current 1 2 is flowing through the load.

,The charging circuit for the capacitor C 3 is comprised of the second-ary winding STC, of the transformer TC, which is `connected through the diode D S to charge the capacitor C 3. The primary winding PTC of the transformer TC and a diode 206 are connected between the positive power terminal 12 and the second load terminal 20. Therefore, the primary winding PTC is connected in shunt around the power SCR P 2 and in parallel with the load 16 when the current 1 1 is flowing through the load.

The charging circuit for the capacitor C 4` comprises the secondary winding STD of the transformer TD which is lconnected through the diode D 4 to charge the capacitor C 4. The primary winding PTD of the transformer TD and a diode 208 are connected between the positive power terminal 12 and the first load terminal 18. Therefore, the primary winding PTD is connected in shunt around the power SCR P 1 and parallel to the load 16 when'the current 1 2 is flowing through the load.

The oper-ation of the changing circuits will best be Lunderstood by an explanation of the operation of the entire inverter device. As previously mentioned, the eight secondary transformer windings which control peration of the eight SCRs are identical to those shown in FIGURE 2A and therefore have the same operating time sequence when actuated by control signals t) and 54. At time To, power SCRs P 1 and P 3 are turned on by positive trigger pulses induced in the secondary control windings SP-1 and SP-3. A current 1 1 then ows through the load 16 as indicated, so that the load terminal 18 assumes substantially the positive potential ofthe power terminal 12 and the terminal 20 assumes the negative potential of :the power terminal 14. The current 1 1 will also flow fromv the positive power term-inal 12 through the primary winding PTC and through the diode 206 to the negative load terminal 20. The rise kin the current 1 1 in the primary winding PTC will induce a current inthe secondary windingSTC which will charge the capacitor C-S through the diode D 3. 1t will be note-d that the capacitor O-S will be charged at time To (see FIG. 1A) when the power SCR P 3 is 1"-1 triggered on so that the capacitor C-3 is properly charged to reverse bias the power SCR P 3 to cutoff at time T1.

When the current 1 1 is flowing, the first lo-ad terminal 18 is positive with respect to the negative power terminal 14. rTherefore, the current 1 1, in addition to flowing through the load 16, also passes through the diode 262 and through the primary winding PTA of the transformer TA to the negative power terminal 14. As the current 1 1 rises in the primary winding PTA, a charging current is induced in the secondary winding STA which charges the capacitor C 1 through the diode D l. Therefore the capacitor C 1 is charged each time the power SCR P-1 is triggered on preparatory to reverse biasing the power SCR P 1 to cutoff At time T1 (See FIG. 1A), positive trigger pulses are induced in the secondary windings SRE-1 and SRE-3 to trigger the reverse bias SCRs RB 1 and RB 3 on The capacitors C 1 and C 3 then discharge and reverse ibias the power SCRs P-1 and P 3 to cutoff Also at time T1, plus a short delay as hereafter described in connection with FIGURES 5 and 6, the secondary transformer windings SP-2 and SP 4 provide a positive trigger pulse to trigger :the power SCRs P 2 and P 4 on A current 1 2 will then iiow through the load 16 as indicated and the second load terminal 20 will become positive and the first load terminal 18 will become negative. Since the second load terminal 2i] is positive with respect to the negative power terminal 14, a portion of the current 1 2 will pass through the diode 204 and through the primary winding PTB of the transformer T B. As the current 1 2 through the primary winding PTB rises, a charging current will be induced in the secondary winding STB which will charge the capacitor C 2 through the diode D 2. Similarly, since the iirst load terminal 18 is negative with respect to the positive power terminal 12, a portion of the current 1 2 will pass through the primary winding PTD of the transformer TDand through the diode 208 to the load terminal 18. As the current 1 2 through the primary windings PTB rises, fa current will be induced in the secondary winding STD which will charge the capacitor C 4- through the diode D-4. Therefore, the capacitors C 2 and C 4 will be charged preparatory to reverse biasing the power SCRs P 2 and P 4 to cutofff At time T2 (see FIG- URE lA), a positive trigger pulse will beinduced in the secondary transformer windings SRE-2 and SRE-4 to trigger the reverse bias SCRs RB-2 and RB-4 on and discharge the capacitors C 2 and C 4 and thereby reverse bias the power SCRs P 2 and P 4 to cutoff This sequence of events will repeat in synchronism with the control signals 50 and 54 indenitely. When the control signals 50 and 54 are stopped, the fall of the last positive half cycle of each signal will trigger the reverse bias SCRs on to reverse bias the power SCRs to cutofff olf state when the potential from the respective capacitors has dissipated to substantially zero. Therefore all components of the inverter device lautomatically assume the cutolf state upon cessation of the control signal. The eight diodes 220, 221, 222, 223i, 224, 225, 226 and 227 are provided to limit the high reverse voltages which will be induced in each of the transformers by the collapsing magnetic elds caused when the pairs of power SCRs are switched on and on tion of these diodes will be evident to those skilled in the art. It will also be evident that instead :of four separate transformers TA, TB, TC and TD, two centertapped transformers could be used. However, two center-tapped transformers would not have the isolation advantages of the four separate transformers.

Embodment of FIGS. 4 and 4A Referring now to FIGURES 4 and 4A, an inverter device 300 is very similar to the inverter device 200 of The reverse bias SCRs will assume the cut-V The opera- Y Y i i FIGURE 3, except that the primary windings' ofthe capacitor charging transformers are eliminated from the power bridge circuitry `and the secondary windings are inductively coupled to control transformer primary windings which yare energized by the control signal.VV Any 'suitable direct current power supply maybe connected 'Y across the positive power terminal 12 and the negative power terminal 14. Power SCRs P-1,` P-2, P43' and P-4` rare connected to the load 16 and to the power terminals 12 and 14 in the manner previously described to form -a power bridge. Current I-1 will -then flow through the load 16 when power SCRs P-1 and P-S are Y switched on, iand a current I-Z will dow through the load 16 when the power SCRs P-'Z and P-4 are switched VYon, as previously described. Each power SCR has a reverse vbias circuit lcomprised of aY capacitor anda ref.

verse bias- SCRy as previously described. For example, SCR RB-lrcontrols the discharge of capacitor C-l for reverse biasing power SCR P-l to cuto SCR RB-Z controls the discharge of capacitor C-Z for reverse biasing SCR P-2 to cutofrf vSCR RB-3 controls the discharge of capacitor C-3 for reverse biasing power SCR P-3` to cutoff. Similarly, SCR R13-4 controls the discharge of capacitor C4.for reverse biasing power ySCR P-4 to cutoif. The power SCRs P-1, P-Z, P,3 and P-4 are triggered on by positive pulses induced'inthe :secondary .transformer windings SP-1, SP-Z, SP-3 and SP-4, `respectively. The reverse bias SCRs RB-Jl, RB-Z,

RB-3 and RB-4 are triggered on by positive pulses,

Y induced in the secondary transformer windings SRE-1,

SRE-2, SRE-3 and SRE-4, respectively.

Circuit means are provided for charging eachfofthe capacitors to a potential lof a polarity and magnitude suicient to reverse bias the respective power SCRs to cutolf upon discharge of the respective capacitor. A secondary winding SC-1 of a control transformer CT-3 (see FIGURE 4A) is connected to charge the capacitor C-1 through a diode D-l.

The secondary Winding VSC-Z of the control transformer CT-4 is connected to charge the capacitorY C-Z through the diode `D-Z. yThe second- Y ary winding SC- of the control transformer CT-S'is connected to charge the capacitor C--S` through the diode D-3. The secondary winding SC-j4 of the control trans- Y former VCT4 is connected to charge the'capacitor' C-4 through the diode D-4.' It'will` be noted that the secondary windings SC-l and SC-3 are inductively coupled to the primary winding of control transformer CT-S and` thatthe secondary winding SC-Z and SC-4 are induc-V i nal 54 in the primary windings of the transformer CT-4.

Therefore, the current of proper polarity is induced in Vthe secondary windings SC-l and SC-3 so as to charge the respective capacitors C-1 and C-3 at time T0, which `correspondsr to the time when the powerSCRs P-l and P-3 are triggered on The capacitors C-1 and C -S then be properly charged to reverse bias the .power SCRs P1 and P--3V to cutoi when the reverse bias 'SCRs RB-l and'RB-S are triggered lon at time T1. Similarly, the secondary windings `SC-Z and SC-4 are inductively coupled `to the primary windings of the control transformer CT-4 in such a manner as to produce a positive pulse at thetime T1 during :the .rise of control signal 54.` The time T1 correspondsto the time the power SCRs P-2 and P-4 lare triggered on so that the capacitors 'C-Z and C-4will then be properly charged to reverse bias the power SCRs P-Z and P-4 to cutoff at time T2, which, of course, is the time the reverse bias SCRs RB-.Z and R13-'4' are triggered .on .to discharge the respectivecapacitlors; Y

The operation of the inverter device of FIGURE 4 is substantially identical with the three previous embodiments described insofar as the switching sequence of the various SCRs is concerned. During the rst rise at T0 inthe first control signal 50, which is applied to the pri-V mary winding ofV transformer CT-S, a positive pulse will be induced `in secondary windings SP-1 and'SP-S to trigger the power SCRs rP-1 yand P-3 ont The current I1 will then dowin the direction indicated bythe arrow through the load 16; Also during the ffirst rise .at time T0 of the rst control signal 50, a positive current will be induced in secondary windings SC-1 and SC-3 and the capacitors C-l and .C-rwill be charged through the diodes D--1 and D43, respectively; Next, during the fall ofthe signal current 50 in the primary winding at timer T1, a Vpositive trigger pulse will be induced in the secondary windings SRB-l .and SRB-3 which will trigger the reverse ybias SCRs RB-land RB-3 on The capacitorsV Y C-1 |and C-3 will then 'discharge in opposition to the power SCRs P-1 Iand P-S t-o reverse bias the respective power SCRs to cutoi During the rst rise, aft time T1, in the secondcontrolv signal 54, which is connected `to the primary winding of the transformer yCT-Z,` a positive pulse will be induced in the secondary windings SP-2` @and Y,SP-4 to triggerthe A power YSCRs 139-2 -and Pr-4 .on. A current `1-2 will then ilow inthe direction indicated by the arrow rthrough the load 16. The same rise of thekcontroi signal54` at the time T1 will induce aacurrent in the secondary windings SC-Zf-and SC-4 which willcharge thecapacitorsi C-2 and C-4, respectively, through the diodes D-Z and D4, respectively. 'Ihe fail iat time T2 of the second con-.1` trol signalY 54 induces -a positiveatrigger pulselrin the secondary windings SKB-2 and SRE-4 `to trigger the reverse bias SCRs RB-2 and RB-4fon. The'capacitors lCdlrand, C4 then discharge to reverse bias the power SCRs P-Zand P-4 to cutoi the load. Upon cessation of the twoV control signals, it will be noted that Yall SCRs are in the cutoif state, yas

previouslydescribed inconnection withtheernbod-iments of FIGURES 1, Zand 3. Y

The operations of the inverter devices of FIGURES l, 2, 3 and 4 have heretofore been described by reference to the simplified control signal representation of YVFIGURE, lA.` In FIGURE lA itis assumed thatat time T1 the first control signal 50y falls simultaneously with the rise of the .second control signal 54. This would result in the power SCRs P-Zrand P-4 V'being triggered on Iat'the same Vinstant thatthe reverse bias SCRs RB-l and RB-3 would be `triggered on to reverse bias the power SCRs P-1 and P. However, even when the power SCRs iare reversed biased to switch the power SCRs to cutoi in a minimum time, a certain finite time period is required before the respective power I SCRs can Vhe switched to cutofli` and it is highly desirable that the pair of power SCRs P-l and P-a, for example, be switched completely to"cutolf before the pair of power SCRs P-Z and P-4 are triggered fon. rllherefore, a slight time delay (t) (see FIGURES 5 and 6) is preferably provided between the instant the reverse Y bias SCRs aire triggered on to reversefhias the power VISCRS, and the instanttihe :next pair of power SCRs Y are triggered on in order tio insure that :adequate time Y So long as the w oontrolsignals continue, this'switching `sequence willw continue Ito produce an `aiternating power currentfthrough FIGURE 5, lines (c) and (d).

iustify the adde-d expense ott the more sophisticated control system (not shown). As previously mentioned, the first and second control signals 50 and 54 are 180 degrees out-of-phase. During the rise of the first control signal 50 at time To, positive trigger pulses will be induced in the secondary windings SP-l and SP-3 as shown in The positive trigger pulses illustrated are induced -in the secondary windings SP-1 land SP-3 of the `inverter devices of lFIGURES 2, 3 yand 4 and in the corresponding secondary windings of transformers TP-l Vand 'TP-3 in the inverter device of FIGURE l. As previouslyl described, the positive potential generated in the secondary windings SP-l and SPS trigger the power SCRs P-l Iand P-Z on At time T1 the first control signal 50 falls and thereby induces a negative potential in the secondary windings SP-l and SP-3. Since the negative potentials are of no corrsequence to the loperation of the respective SCRs, no further reference will be made to negative potentials induced in fthe various secondary windings. However, the secondary windings SRE-1 andV SRB-3 are wound in such a manner that a positive trigger pulse will be induced therein by the fall of the first control signal 50 at time T1, as shown `at lines (e) and (f) of FIGURE 5. The positive pulses induced in the windings SRB-l and SRB3 trigger ihe reverse bias SCRs RB1 `and RB-S on and thereby discharge the capacitors C-1 and C-S and reverse 'bias the power VSCRs P-l and P-3 to cutoff lf the rise of the second control signal 50 occurred at precisely the same time as the fall of the first control signal 50, the power SCRs P-1 and P-3 would not be completely switched to cutoff before the power SCRs P-Z and P-4 would be switched on because the trigger pulse applied to the gate of an SCR switches the SCR on considerably faster than a reverse bias from cathode to anode can switch the SCR to cutoff Therefore, it will be noted that the rise of second control signal 54 trails the `fall of the first control signal 50 by a short time delay indicated by the reference character (t). Therefore, at time T1 plus (t) the rise in the second control signal 54 induces a pulse of positive potential in the secandary windings SP-Z and SP-4 as illustrated at lines (g) and (h) of FIGURE 5. These positive pulses trigger the power SCRs P-2 and P-4 on as previously described. However, the short time delay (t) provides suicient time for the power SCRs P-1 and'P-Z to be reverse biased to cutoff by discharge of the capacitors C1 and C-Z as previously described before the power SCRs P-2 and P44 are triggered on The fall of the second control signal 54 at time T2 induces positive pulses in the secondary windings SRB-Z and SRE-4 which trigger the reverse -bias SCRs RB-Z and RB-4 on and thereby discharge the capacitors C-Z and C-4 to reverse bias the power SCRs P-2 and P4 to cutoff The short time delay (l) later the rst control signal Si) again rises, at time T2 plus (t), and again induces a positive trigger pulse in secondary Windings SP-l and SP-3 to trigger the power SCRs P-1 and P-S on However, the power SCRs P-Z and P-4 have had suilicient time to revert to the cutoff state as a result of the applied reversed bias. The resulting current through the load 16 is shown at line (k) of FIGURE 5 and comprises a square wave current having a spacing or time delay (t) between the positive and negative going portions of the alternating current. In summary, it will be noted that events 4atti, #2, #3 and #4 occur sequentially at times T0, T1, T1 plus (t) and T2 and will repeat so long as the control signals 5.0 and 54`are applied to the primary windings of the control transformers.

As previously mentioned, a pair of sinusoidal control -signals 50a and 54a (see FIGURE 6) can be used to trigger the several inverter devices in substantially the same manner as the square wave control signals; 50 and 54, with the exception of the devices described in FIG- URE 4 and FIGURE 4a. The sinusoidal control signals and the resulting currents or potentials induced in the various secondary windings are schematically illustrated in FIGUREv 6 in which the various curves are aligned 'with the corresponding curves of FIGURE 5 lfor convenience of illustration. It will be noted that the first control signal 50a is 180 degrees out of phase with the second control signal 54a, and that both the first and second control signals are in phase with the voltages of subsequent signals induced in the various secondary windings. Therefore, it will be noted that during the positive half-cycles of the signal 50a from time T o to time T1, positive half-cycle trigger pulses will be induced in the secondary windings SP-l and SP-3 as shown at lines (c) and (d) of FIGURE 6, to trigger the power SCRs P-l an-d P-3 on Corresponding negative half-cycle pulses are induced in the secondary windings SRB-l and SRR-3 during the period T1-T2, but will be disregarded because negative potentials have no effect upon the operation of the various SCRs. During the negative half-cycle of the control signal 50a from time T1 to time T2, a positive fhalf-cycle pulse is induced in the secondary windings SRB-l and SRE-3 to trigger the reverse lbias SCRs RB-l and RB-3 on to thereby discharge the capacitors C-1 and C-3 and reverse bias the power SCRs P-l and P-3 to cutoff ,Since the secondary windings SP-Zl and SP-4 are inductively coupled to the second control transformer CT-Z, the positive half-cycles of the second control signal 54a will induce a positive half-cycle trigger pulse in the secondary windings SP-2 and SP-4 beginning at times T1 and T3, as indicated at lines (g) and (h) of FIGURE 6, to trigger the power SCRs P42 and P-4 on Similarly, the negative half-cycles of the control signal 54a will induce a positive trigger pulse in the secondary windings SRE-2 and SRB-4 at time T2 to trigger the reverse bias SCRs RB-2 and RB-4 on to discharge the respective capacitors and reverse bias the power SCRs P-Z and P-4 to cuto 'As previously discussed with regard to FIGURE 5, it is desirable to provide a time delay (t) between the time that the reverse bias SCRs RB-l and RB-S, for example, are triggered on to discharge the capacitors C-1 and C-3 and apply a reverse bias to the power SCRs P-l and P-3, and the time the next pair of power SCRs P-2 and P-4 are triggered on This time delay (z) provides an opportunity for the power SCRs to be competely cutoff as a consequence of the applied reverse bias before the next succeeding pair of power SCRs are triggered on. The time delay (t) can be provided by controlling the potential or trigger level at which the Various SCRs will be triggered on This is easily accomplished by making the trigger level or potential at whichrthe power SCRs P-1, P-Z, P-3 and P-4 will be triggered on higher than the trigger level or potential at which the reverse bias SCRs RB-l, RB-Z, R13-3 and RB-4 will be triggered on The manner in which the time delay (t) is provided can readily be seen from a comparison of lines (e) and (f) of FIGURE 6 with lines (g) and (h). The potentials induced inthe secondary windings SRB-l and SRB-3, lines (e) and (f), are irl-phase with the potentials induced in the secondary windings SP-Z and SP-4, lines (g) and (h). However, since the trigger levels for SCRs RB-l and RB-3 are below the trigger levels for SCRs P-Z and P-4, as the induced potentials `rise, the SCRs RB-l and RB-S will be triggered on a period of time (t) before the power SCRs P-Z and P-4 are triggered on This provides a period of time which assures that the power SCRs P-1 and P-3 are reverse biased to cutoff before the power SCRs RB-Z and RB-4'were triggered on The same time delay exists between the time Kthe reverse bias SCRs RB-'Z and RB-4 are triggered on and the time the power SCRs P1 and P-3 are triggered back on, as can be seen by a comparison of `lines (i) and (j) with lines (c) and (d),

at time T2, for example. y. Therefore-as when the squarewave control signals are used, thel resulting power current throughthe load 1.6 is a square wave alternating current having a time delay (t) between successive positiveV polarity of the secondary windings ofV thecontrol transt formers. It will. also be evident that since the sinusoidal control signals 50a and 54a are identical, but 180 outof-phase, a single sinusoidal control signal could be used and applied to either a single primary winding of a single control transformer, or to both primary windings of transformers CT-l and CT-Z, or CT-3 and CT-4, provided that the polarity of all the secondary windings in transformers CT-2 and CT-4 is reversed.

From the above detailed description Vit will be evident that an improved inverter device `for converting a direct current power supply to an alternating current power supply having a frequency which is synchronized with that of a control signal has been described. The frequency of the alternating current produced is variable over a wide range. The inverter device has an increased power` rating, the rating `for a sample inverter being on the order of 28,000 watts as compared to approximately 1,000 watt maximum power ratings of previously used power amplifierr devices. The inverter device produces a n square-wave power current for maximum power yield for a given direct current potential. The inverter devicer oit is used to charge the capacitors.

Having thus described various embodiments of lour invention, it is to be understood that various changes and substitutions can be made therein without departing from the spirit and scope of our invention as defined by the appended claims.

. We claim:

1. Asynchronous inverter `device for converting 'direct current to alternatingycurrent for drivinga loadbaving Yfirst and secondpterminals, ythe inverter device employing a plurality of controlled rectifier -devices each having a cathode, an anode and agate, each controlled rectifier having the characteristics of blocking current in either the. f forward-or'reverse directions untilga trigger pulseisY applied to the gate, then Yconducting conventional current in the forward direction from the anode to the cathode until a reverse bias is applied from the cathode to the anode, and then assuming the forward and reverse Vcurrent blocking characteristic again, the inverter deviceV comprising:

Y a first controlled rectifier, the lirst load terminal and a fourth controlled rectifier connected in series in the forward direction across a direct current powerv source; y a second controlled rectifier, the second load terminal current to alternating current for driving a load as de- 20 a reverse bias to the first and third controlled rectiiiers for restoring the forward and reverse current blocking condition of each;

. a trigger pulse to the second and fourth controlled rec-V l -tiers for causing conduction of each in the forward I direction; Y and, a reverse bias to the second and fourth controlled frectiiiers `for restoring the forward and reverse current blocking condition of each; whereby the direct current power source will alternately berapplied to the loadin one direction through the first and third controlled rectifiers and in the other direction through the second and fourth controlled rectiiiers. Y 2. A synchronous inverter device for converting direct current to alternating current for driving a load as delined in claim 1 wherein:

the control circuit means is characterized lby a capacitor connected across the anode and cathode of each of l,the controlled rectitiers, means for charging the capacitors to a potential of a polarity (and magnitude sutlicient to reverse biasthe controlled rectiiiers to the current blocking condition upon discharge thereand means for discharging the respectiveV capacitors to Ireverse bias the Vcontrolledy rectiers in the proper sequence.

3. A synchronous inverter device for convertingdirect current to alternating current for driving a load as defined in claim 2 whereinV the means for charging the capacit-ors to |a potential of ka polarity and magnitude sufficient to reverse bias the controlled rectiiiers to the current blocking condition upon discharge thereof are characterized by: Y y a transformer the primary windingY of which is connectedin series with theV load t-o receive the current passing through the load and the secondaryv winding of Iwhich is connected Vthrough a diode to change the capacitor.

4. A synchronous inverter device for converting direct Y fined rin claim 2 wherein the means for Vcharging the Vcases, the potential of thepower source being switched and Ya third controlled rectier connected in series in f Vthe forward direction across the direct current power source; and, i a .control circuit means for' sequentially applying: a trigger pulse to the irst and third controlledrectitiers for causingA conduction of each in the forward directiom capacitors to a potential of a polarity and magnitude sufficient to reverse bias the controlled reotiiiers to the current lblocking condition upon discharge thereof are characterized by: f Y

an alternating current source connected through a diode to partially change the respective capacitors, the capacitors being connected to aload terminal whereby the capacitors will be further charged to magnitude by the drop in.V

the necessary reverse kfbias potential across'the load. v 5. A synchronous inverterdevice for convertingfdirect eurrent'to -alternating current for'driving `a load as defined in claim 2 wherein the means .for charging the capacitors to la potential of a polarity and magnitude Y sufficient to reverse bias the controlled rectiiiers to the Y current blocking condition upon discharge thereof- Aare characterized 'by Acapacitors land the primary winding of which is energized by lan alternating current control signal also utilized for controlling the sequencey of the control circuit means.

a transformer the secondary winding of which is con- Y nected throughy a diode to chargev the respective 7. A synchronous inverter device for converting direct current `to alternating current for driving a load las defined in claim 1 wherein the control circuit means is characterized Fby:

'a capacitor and an additional controlled rectifier connected in series across the `anode and cathode of each of said first, second, third and fourth rectifiers, each additional controlled rectifier being connected in opposition to each of said fourV controlled recti- V fiers for applying a discharge from the respective capacitor to reverse Ibias each of said lfour controlled rectifiers;

circuit means for charging each of the capacitors to a potential of a polarity and magnitude toreverse lbias each of said four controlled rectifiers when discharge-d; and,

circuit means for applying a trigger pulse to each of the additional controlled rectiiers tto disch-arge the respective capacitor and reverse bias each of said controlled rectifiers in the proper sequence.

8. A synchronous inverter device for converting direct current to alternating current for driving -a load as defined in claim 1 wherein the control circuit means is characterized by:

subcircuit means for applying a reverse -bias to each of said first, second, third and fourth controlled rectifiers comprising a capacitor and an additional controlled rectifier connected in series across the anode and cathode of each of said first, second, third and fourth controlled rectifiers, the additional controlled rectifiers being connected in opposition to said first, second, third, `and fourth controlled rectifiers;

subcircuit means for charging the capacitors to a potential of a polarity and magnitude -sufiicient to reverse bias each of the said four controlled rectifiers when discharged, tand `lsu-ocircuit means for applying a trigger pulse to each Y of the additional controlled rectifiers for causing the additional controlled rectifiers to conduct and ydischarge the respective capacitors `and thereby reverse bias each of the said first, second, third `and fourth controlled rectifiers in the proper sequence.

9. A synchronous inverter device for converting direct current to alternating current for driving la load `as 'defined in claim 1 wherein the control circuit means is further character-ized by:

circuit means for producing Vfirst `and second alternating current control signals 1S() degrees out of phase;

circuit means for producing ,a positive pulse responsive to the rise of the positive half-cycle of the first control signal for applying a trigger pulse to the first and third controlled rectifiers;

circuit means for applying a reverse bias to the first and third controlled rectiers responsive to the fall of the positive half-cycle of the first control signal;

circuit means for producing a positive pulse responsive to the rise of the positive Vhalf-cycle of the second control signal for applying a trigger pulse to the second tand fourth controlled rectifiers; and,

circuit means for applying a reverse bias to the second and fourth controlled rectifiers responsive to the fall of the positive half-cycle of the second cont-rol signal.V l

10. A synchronous inverter device for converting direct current to alternating current for driving a load having first and second terminals, the inverter device employing a plurality of silicon controlled rectifier semiconductor devices known as SCRs each having a cathode terminal,

, an anode terminal and a gate terminal and having the characteristics of normally remaining cutoff to block current in either the conventional forward or reverse directions until a positive trigger pulse is applied to the gate terminal, then being turned on7 for conducting conventional current in the forward direction from anode to the cathode until a reverse bias is applied from cathode to anode, and then assuming the cuto condition to block the forward and reverse current, the inverter device comprising:

a first power SCR, the first load terminal, and a fourth power SCR connected in series in the forward direction across a direct current power source;

a second power SCR, the second load terminal, and a third power SCR connected in ser-ies in the forward `direction across the direct current power source;

a reverse bias circuit comprised of a capacitor and a control SCR connected in series across the anode and cathode of each of the power SCRS, the control SCRs being connected to opposition to the power SCRS whereby when the control SCRS are turned on the capacitors will be discharged to reverse bias the respective power SCRs;

circuit means for charging the capacitors to a potential of a direction and magnitude to reverse bias the respective power SCR through the reverse bias circuit upon discharge thereof;

and control circuit means for sequentially:

applying a trigger pulse to the gates of the first and third power SCRs for turning the first and third power SCRs on;

applying a trigger pulse to the control SCRs for the first and third power SCRs for turning the control SCRS on and thereby discharging the respective reverse bias capacitors to reverse bias the respective power SCRs to cutoff;

applying a trigger pulse to the gates of the second and fourth power SCRs for turning the power SCRS on; and,

applying a trigger pulse to the gates of the control ,SCRS for the second and fourth power SCRs thereby turning the control SCRs on and discharging the respective reverse bias capacitors to reverse bias the respective power SCRs to cutoff whereby the direct current power source will be passed first in one direction through the load by the first and third power SCRs and then in the other direction by the second and fourth power SCRs.

11V. A synchronous inverter device for converting direct current to alternating current for driving a load as defined in claim 10 wherein the control circuit means is characterized by:

circuit means for producing first Iand second alternating current control signals degrees out-of-phase;

first and second transformers having first and second primary windings, respectively, the first primary winding being connected to the last mentioned circuit means for receiving the first control signal and the second primary winding being connected to the last mentioned circuit means for receiving the second control signal;

a secondary winding of the first transformer connected to apply a positive trigger pulse to the gate terminal of the first and third power SCRs during the rise of the first [control signal;

a secondary winding of the first transformer connected to apply a positive trigger pulse to the gate terminals of the control SCRs for the first and third power SCRS during the fall of the first 'control signal;

a secondary winding of the second transformer connected to apply a positive trigger pulse to thegate terminals of the second and fourth power SCRs during the rise of the second control signal; and,

a secondary winding of the second transformer connected to apply a positive trigger puise to the gate terminals of the control SCRS for the second and fourth power SORs during the fall of the second control signal.

12. A synchronous inverter device for converting direct current to alternating current for driving a load as defined in claim 10 wherein the circuit means for chargdischarge thereof are characterized by:

the primary winding of a transformer connected inV l series between the load and the respective power SCR; and,

the secondary windingfof the transformer is connected through a diode to charge the respective capacitor, the secondary winding and diode being connected in shunt'around the respective control SCR;

the polarity of the primary -and Ysecondary windings and therdirection of the diode being such that upon conduction of the respective power SCR, the risey of the power current through the primary winding of the respective transformers'will induce Ya current in the respective secondarywinding which will pass through the respective diode and charge the respective capacitor. 13. A synchronous inverter device for converting direct current to alternating current for driving a load asfdeined in claim wherein the circuit means `for charging the capacitors to aV potential of a direction Aand magnitude to thereof are comprised of:

` rst and second autotransformers;

the primary winding of the lirstautotransformer Vbeing connected betweenV the first ioadt'erminal and the Vnectedin Vshunt around the Vcontrol SCR in the reversen bias circuit for the rst power SCR;

fr a fourthdiode connected between the secondary Winding of the first autotransformer and the capacitor in the reverse lbias circuit for the fourth power SCR whereby the current induced in the secondary winding t when the yfourth power'SCR is turned on will charge s the capacitor for Vthe fourth ypower SCR, the `Secondary winding of the ti-rst autotransformer andthe fourth diode being connected in shunt around the con- -trol SCRV in the reverse bias circuit for the fourth power SCR; Y Y l y the secondary winding of the second autotransformer and a third diodeconnected in series between the second load terminaland ythe capacitor in the control circuit for the` third power SCR,V whereby the current induced kin the secondary winding when lthe third power SCRy is turned on will charge the capacitor for the third power SCR, the secondary winding of the secondautotransformer and the third diode being connected in shunt around the control SCR in the reverse bias circuit for the third power SCR; and,

` reverse bias the respective-power SCRs upon discharge -a second diode connected Abetween the secondary windt ing of the second autotransformer and the capacitor Y inthe reverse bias -circuit for the second power SCR whereby the currentfinduced in the secondary windf Ving when the second powerSCR is turned on will charge the capacitor` for the second power SCR; thesecondary winding of the second autotransformer and l the second ydiode being connected in shunt around theV control SCR'in the reverse bias circuit for the secondpower SCR. v

14. A synchronous inverter device for converting dire-ct i current to alternating current for driving a load as defined` 2d the circuit means for charging the capacitors to a potential of a direction andmagnitude. to reverse bias the respective power SCRs upon'discharge thereof Y comprises;

circuit means connecting a diode, la resistor and the respective 'capacitor in series across the alternator for applying anxalternating` current to the capacitor, the diode being directed to permit charging ofthe respective capacitors in a direction for discharge through the reverse bias circuit capacitors in opposition tothe y t respective power SCR; and,

one side ofthe respectivecapacitor is connected directly to a load terminal, f f

whereby the' Yrespective rcapacitors will be partially Vcharged through the respective diodes by the voltage from the alternator and the charge will be approximately doubled when the respective power SCR is turned on due to the volt-age drop across the load.

15. A synchronous inverter device forv converting` direct thereof are characterized by:

a secondary transformer winding connected through a diode to charge each capacitor; tirst primary transformer windings` inductivelyY coupled to the secondary transformer windingswhich `are connected to charge thecapacitors of the reverse bias l circuits for the first and third power SCRS, the tirst primary transformer windings being connectedparallelto the load when the -iirst and third power SCRs `are turned on, whereby the power current will pass through both the load and the first primary windings when the first andthirdrpowerV SCRs are turned fon and the rise in current through the primary windings will induce a current in the respective secondary windings to charge the respective capacitors;

second primary transformerwindings inductively couf pled to the secondary transformer windings which ,n

ond primary windings ywhen the secondand fourth Y l power SCRs are turned on Iand the rise in current through theprimar'y'A winding whenV the ysecond and;

' fourth power SCRs are turned on will induce a current in the respective secondary windings to `chargey t rthe respective capacitors. f f

' 16. A synchronous inventer device for converting `direct current Vto alternating current for driving `afload as defined in claim 10 wherein the circuit means for charging the capacitors'to a kpotential ofV a direction and magnitude to reverse `bias the respectiverpower- SCRS upon dis,- charge thereof are characterized by: y

a first transformer, the secondary winding of which is connected through a diodey to charge the capacitorV for reverse ,bia-sing the firstv power SCR 4and the primary winding of Whichis connected `in shunt around the fourth power SCR; Y

al fourth transformer, the'secondary winding of which f is connected through a diode to charge the capacitork v Y for reverse biasing the second power SCR and the primary winding of whichis connected in shunt K around the third power SCR; and,' a third transformer, the secondary winding of which is connected through .a diode to charge the capacitor 25 for reverse biasing the third power SCR and the primary winding of which is connected in shunt around the second power SCR.

17. A synchronous inverter device for converting direct current Ito alternating current for driving a load as dened in claim 11 wherein the circuit means for charging the capacitors to -a potential of `a direction and magnitude to reverse bias the respective power SCRs upon discharge thereof are characterized by:

a secondary winding of the rst transformer connected through a diode Ito charge the capacitors for reverse biasing the first and third power SCRs, the second- :ary Winding being connected to charge 'the capacitors by the current induced therein during the rise of the first alternating current control signal;

a secondary winding of the second transformer connected lthrough a diode to charge the capacitors connected to reverse bias the second and fourth power SCRs, the secondary winding being connected to charge the capacitor by the current induced therein during the rise of the second alternating current control signal.

References Cited kin the ile of this patent UNITED STATES PATENTS 2,987,666 Manteuffel June 6. 1961 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 103,616 September lO, 1963 Jimmy R. Cole et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 6OI for "locking" read blocking column 5, line 30 before "reverse" strike out "the"; column lO, lines 54, 55 and 60, for "resister" read resistor column 1l, lines 32 and 39, for resisters" read resistors Signed and sealed this 7th day of July 1964.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Auesting Officer Commissioner of Patents 

1. A SYNCHRONOUS INVERTER DEVICE FOR CONVERTING DIRECT CURRENT TO ALTERNATING CURRENT FOR DRIVING A LOAD HAVING FIRST AND SECOND TERMINALS, THE INVERTER DEVICE EMPLOYING A PLURALITY OF CONTROLLED RECTIFIER DEVICES EACH HAVING A CATHODE, AN ANODE AND A GATE, EACH CONTROLLED RECTIFIER HAVING THE CHARACTERISTICS OF BLOCKING CURRENT IN EITHER THE FORWARD OR REVERSE DIRECTIONS UNTIL A TRIGGER PULSE IS APPLIED TO THE GATE, THEN CONDUCTING CONVENTIONAL CURRENT IN THE FORWARD DIRECTION FROM THE ANODE TO THE CATHODE UNTIL A REVERSE BIAS IS APPLIED FROM THE CATHODE TO THE ANODE, AND THEN ASSUMING THE FORWARD AND REVERSE CURRENT BLOCKING CHARACTERISTIC AGAIN, THE INVERTER DEVICE COMPRISING: A FIRST CONTROLLED RECTIFIER, THE FIRST LOAD TERMINAL AND A FOURTH CONTROLLED RECTIFIER CONNECTED IN SERIES IN THE FORWARD DIRECTION ACROSS A DIRECT CURRENT POWER SOURCE; A SECOND CONTROLLED RECTIFIER, THE SECOND LOAD TERMINAL AND A THIRD CONTROLLED RECTIFIER CONNECTED IN SERIES IN THE FORWARD DIRECTION ACROSS THE DIRECT CURRENT POWER SOURCE; AND, CONTROL CIRCUIT MEANS FOR SEQUENTIALLY APPLYING: A TRIGGER PULSE TO THE FIRST AND THIRD CONTROLLED RECTIFIERS FOR CAUSING CONDUCTION OF EACH IN THE FORWARD DIRECTION: A REVERSE BIAS TO THE FIRST AND THIRD CONTROLLED RECTIFIERS FOR RESTORING THE FORWARD AND REVERSE CURRENT BLOCKING CONDITION OF EACH; A TRIGGER PULSE TO THE SECOND AND FOURTH CONTROLLED RECTIFIERS FOR CAUSING CONDUCTION OF EACH IN THE FORWARD DIRECTION; AND, A REVERSE BIAS TO THE SECOND AND FOURTH CONTROLLED RECTIFIERS FOR RESTORING THE FORWARD AND REVERSE CURRENT BLOCKING CONDITION OF EACH; WHEREBY THE DIRECT CURRENT POWER SOURCE WILL ALTERNATELY BE APPLIED TO THE LOAD IN ONE DIRECTION THROUGH THE FIRST AND THIRD CONTROLLED RECTIFIERS AND IN THE OTHER DIRECTION THROUGH THE SECOND AND FOURTH CONTROLLED RECTIFIERS. 